The present invention relates to a main bearing for an engine, which supports a crankshaft on which a radial load always operates in a single direction owing to tension of a belt installed for transmitting rotation, and more particularly to a main bearing for an engine, which improves wear resistance and an anti-seizure property of a portion taking the radial load in a single direction.
In an automobile gasoline engine, for example, a camshaft, an alternator, a compressor for an air conditioner or the like are driven by utilizing the rotation of a crankshaft. The crankshaft is connected with the camshaft through a dogged belt and with the alternator and compressor through V-belts for transmitting the rotation.
On the cogged belt and V-belt, a predetermined tension is applied in order to prevent tooth skipping, slippage, or the like. Because of the tension applied on the cogged belt and V-belt, the crankshaft takes a radial load, and the radial load is received by a main bearing which supports the main shaft portion of the crankshaft.
The direction of the resultant force of the radial loads operating on the crankshaft by the tension applied to the cogged belt and the V-belt or the like is opposite from that of a combustion pressure (normally, downward in a vertical type engine) operating on the crankshaft from a piston through a connecting rod during the run of the engine, whereby a load operating in the same direction with a combustion pressure is eliminated in order to prevent the specific load on the main bearing from growing excessively, so that the bearing service life is lengthened.
Tensions of a cogged belt and V-belt always operate on a crankshaft, and when an engine stops, a main shaft portion of the crankshaft will be pressed against a main bearing owning to a radial load resulting from the tensions of the above described belts. when the engine stops, an oil pump will also stop and then the supply of lubricant to the main bearing will be cut off. By this reason, a film of oil on the main bearing surface is broken by the above described radial load always operating on the crankshaft, and the main shaft portion of the crankshaft will be brought into direct metal contact with the main bearing surface.
When the engine restarts, the oil pump will also start. However, lubricant will be supplied late from the oil pump to the main bearing. Thus, the main shaft portion of the crankshaft will rotate in an incomplete lubricated state, whereby there is a possibility of the seizure as well as the increase of wear of the main bearing.
Especially in recent years, a vehicle which stops the engine when stopping at a crossroad and a hybrid car using both an engine and an electric motor have come into the market in order to prevent the exhaust of combustion gases causing environmental pollution as much as possible. The engine used in such a vehicle frequently repeats a start and a stop, and is also required to rotate at high revolution beyond a range of an idle engine revolution immediately after the start. Moreover, in such an engine which frequently repeats a start and a stop, there is a need to tighten a cogged belt and a V-belt to high tension to prevent tooth skipping and slippage of these belts more reliably. Because of this reason, the main shaft portion of the crankshaft frequently rotates in a metal contact state with the main bearing or in an incomplete lubricated state, and in some cases, these states cause abnormal wear and seizure.
The present invention has been made in view of the above described circumstances. Accordingly, the object of the invention is to provide a main bearing for an engine which can improve wear resistance and an anti-seizure property of a portion of the main bearing which takes a radial load by tension of a cogged belt or a V-belt.
According to a first aspect of the present invention, in order to achieve the above object, a main bearing is provided with an oil pocket portion for storing lubricant to be supplied to a portion of the bearing surface, against which a crankshaft is pressed by a radial load in a single direction, so that the lubricant stored in the oil storing portion is supplied to the portion against which the crankshaft is pressed by the radial load substantially at the time that the crankshaft starts rotating. Accordingly, a complete lubricated state or almost the same state with that is obtained at the beginning of the start of the engine, and wear resistance and an anti-seizure property of the main bearing are enhanced.
The oil pocket portion may be a plurality of recesses, or may be a plurality of grooves.
Moreover, the oil pocket portion also may be a branch groove formed so as to branch off from an oil groove formed on the bearing surface along its circumferential direction.
Furthermore, in order to achieve the above described object, a second aspect of the present invention is characterized in that linear hard portions are formed in parallel with each other in a portion, against which the crankshaft is pressed by the radial load in a single direction, among circumferential portions of the bearing surface.
According to this constitution, a portion between the hard portions becomes in a concave shape since the relatively soft portion other than the hard portions in the portion against which the crankshaft is pressed by the radial load in a single direction is worn away early by the rotation of the shaft at the beginning of use while the hard portions are difficult to be worn away, whereby lubricant is stored in the recess. Thereafter, lubricant stored in the recess is always supplied to the portion against which the crankshaft is pressed by the radial load nearly at the same time as the shaft starts rotating, whereby excessive wear and seizure of the portion are prevented in the same way as the first aspect of the invention.
A third aspect of the present invention is characterized in that a plurality of concave streaks are formed on the bearing surface along its circumferential direction, and a portion, against which the crankshaft is pressed by the radial load in a single direction, of the bearing surface is formed to be harder than the remaining portions.
According to this constitution, a protruding portion between adjacent concave streaks is difficult to be worn away in the hardened portion and thus the concave streaks remain as they are over a long period of time. As a result, lubricant can be supplied over a long period of time to the portion against which the crankshaft is pressed by the radial load in a single direction.
A fourth aspect of the present invention is characterized in that a recess is formed on the bearing surface in a portion, against which the crankshaft is pressed by the radial load in a single direction, and the recess is provided with a solid lubricant therein.
According to this constitution, the same advantageous effect as that of the first aspect of the invention can be obtained since the solid lubricant is supplied to the portion of the main bearing against which the crankshaft is pressed.